Wind turbine generator torque loads of today are typically implemented as passive resistors having fixed torque curves. If such resistive dump loads are applied as loads to a generator, wear and tear of the resistors and unnecessarily load on the wind turbine drive train often occur.
U.S. Pat. No. 7,605,488 discloses in general terms how to use dump loads for reducing backlashing in wind turbine gearboxes. Apparently, the amount of power being dissipated in dump loads in U.S. Pat. No. 7,605,488 is controlled by varying the degree of which the dump load is active, cf. for example column 3, line 10. Here it is explicitely specified that “ . . . the dump load 5 is partly or fully activated . . . ”. Thus, the amount of power being dissipated is varied by adjusting the capacity of the dump load.
It is a disadvantage of the system suggested in U.S. Pat. No. 7,605,448 that the capacity of the dump load can only be varied in discrete steps. This incremental change (increase or decrease) of the dump load capacity may accidentally induce events that may create load inversions in the gearbox.
It may be seen as an object of embodiments of the present invention to provide a method and a system that allow controlled shutdown of wind turbines so as to avoid backlashing of wind turbine gearboxes, drive train oscillations etc.
It may be seen as a further object of embodiments of the present invention to benefit from the controllability of a generator side converter to ensure controlled shutdown of wind turbines without introducing gearbox backlashing, drive train oscillations etc.